A glass is stated to be moldable when it can be changed in shape under the combined action of temperature and pressure in a mold so as to obtain an article whose surface is a highly precise reproduction of the mold wall, thereby permitting the direct production by molding of spherical and aspherical lenses, for example, with no other finishing operation. Until the present time, only glasses with an alkali metal phosphate or fluorophosphate base, such as those described in U.S. Pat. Nos. 4,285,730, 4,348,484, and 4,362,819 could be considered as moldable.